Conventionally, there is disclosed a power distribution system which distributes an AC power and a DC power in a building such as a house, a shop and an office building in, e.g., Patent document 1. The power distribution system of Patent document 1 includes a distribution board and AC power outlets. Further, DC output power terminals are provided in the AC power outlets, and a transformer and a rectifier are disposed in the distribution board.
In the distribution board, an AC voltage of 100 V or 200 V is converted into three types of AC voltages, e.g., 6 V, 3 V, and 1.5 V, through the transformer, and three types of DC voltages, e.g., 6 V, 3 V and 1.5 V, are acquired by rectifying the three types of AC voltages using a rectifier. The three types of DC voltages produced in the distribution board are distributed to the DC output power terminals.
From the viewpoint of the global environment protection, there has been proposed a power distribution system which performs grid-connected operation of a DC power generation equipment such as a solar power generation apparatus provided in the building and a commercial power source (i.e., an AC power) supplied from a power company (see, e.g., Patent document 2). In such a type of grid-connected system, a DC power generated by the DC power generation equipment is converted into an AC power by a power converter (power conditioner) for converting a DC power into an AC power, and is operated in conjunction with an AC power of the commercial power source. Further, when the power in excess of the power consumed by load in the building is supplied from the DC power generation equipment, a surplus power can be reversely supplied to the commercial electric power source, which is so-called selling of power.